Various types of work machines may be used to transfer bulk material from a work site stockpile and load this material onto transport machines, such as trucks and railroad cars. In many situations, each transport machine may have a particular maximum load capacity determined by a manufacturer's maximum load rating and/or other factors such as, for example, weight restrictions for on-highway vehicles. To promote maximum utilization of the transport machines, it may be desirable to load each transport machine as close as possible to its maximum load capacity. Overloading the transport machines, however, may have negative consequences. Particularly, placing too much weight on a transport machine can significantly increase maintenance costs for the machine. Further, in certain situations, especially to comply with weight restriction regulations, it may be necessary to remove material from an overloaded machine. The extra steps necessary to remove the material can cause costly delays in both the loading and transport processes. Thus, there is a need for systems that accurately and automatically determine the payload weight of a loading machine to ensure that neither too much nor too little material is loaded on a transport machine.
At least one system has been developed for determining the payload weight of a loading machine. U.S. Pat. No. 6,552,279 (“the '279 patent”) issued to Lueschow et al. on Apr. 22, 2003, describes a system for monitoring characteristics associated with a hydraulic cylinder involved in lifting a payload to determine the weight of the payload. Particularly, the system of the '279 patent establishes a first lift curve, including fluid pressure plotted versus extension data for the hydraulic cylinder, by lifting a work implement with no payload. The system then establishes a second lift curve by lifting the work implement filled with a known weight. After this calibration process, the system of the '279 patent can accurately estimate an unknown payload weight by monitoring a third pressure versus extension curve for the unknown payload weight and interpolating or extrapolating a weight value by comparing the third curve to the first and second curves.
The system of the '279 patent can provide accurate payload weight measurements. Nevertheless, the system of the '279 patent may have certain limitations. Particularly, the system of the '279 patent assumes that during the lift of the unknown payload weight, the work implement (e.g., a bucket of a wheel loader or other type of machine) is maintained in an orientation similar to the orientation used during the calibration process. For example, to generate the first and second pressure versus extension curves during the calibration process, the operator may place the work implement in a fully racked back position. If, during the lift of the unknown payload weight, the operator does not maintain the work implement in a similar fully racked position, the resulting payload weight calculation may be inaccurate. This inaccuracy may be due, at least in part, to the center of gravity of the work implement traveling along a different path when lifting the unknown payload weight as compared to the lifts of the known payload amounts.
Other inaccuracies in the payload weight determination may result if an operator fails to perform a suitable calibration process. Specifically, attempting to calibrate the system of the '279 patent on relatively uneven ground where the machine is pitched forward or backward may affect the accuracy of subsequent payload weight measurements. Further, changing the relative work the payload weight measurement.
The present disclosure improves upon the prior art systems for weighing payloads.